Abstract:

A hard bias structure for biasing a free layer in a MR element within a
read head is comprised of a composite hard bias layer having a
Co78.6Cr5.2Pt16.2/Co65Cr15Pt20
configuration. The upper Co65Cr15Pt20 layer has a larger
Hc value and a thickness about 2 to 10 times greater than that of the
Co78.6Cr5.2Pt16.2 layer. The hard bias structure may also
include a BCC underlayer such as FeCoMo which enhances the magnetic
moment of the hard bias structure. Optionally, the thickness of the
Co78.6Cr5.2Pt16.2 layer is zero and the
Co65Cr15Pt20 layer is formed on the BCC underlayer. The
present invention also encompasses a laminated hard bias structure. The
Mrt value for the hard bias structure may be optimized by adjusting the
thicknesses of the BCC underlayer and CoCrPt layers. As a result, a
larger process window is realized and lower asymmetry output during a
read operation is achieved.

Claims:

1. A hard bias structure for providing a longitudinal bias to a free layer
in a spin valve within a magnetic read head, comprising:(a) a first
composite hard bias layer formed on a substrate and on either side of a
spin valve, comprising:(1) a first hard bias layer with a first
thickness, a coercivity (Hc), a top surface, and an Mrt value; and(2) a
second hard bias layer formed on the top surface of the first hard bias
layer, said second hard bias layer has a second thickness greater than
said first thickness, an Mrt value, and a coercivity greater than that of
the first hard bias layer; and(b) a second composite hard bias layer
formed on said first composite hard bias layer, comprising:(1) a third
hard bias layer with a top surface, and a first thickness, coercivity,
and Mrt value essentially the same as that of the first hard bias layer;
and(2) a fourth hard bias layer formed on the top surface of the third
hard bias layer, said fourth hard bias layer has a thickness, coercivity,
and Mrt value essentially the same as that of the second hard bias
layer;wherein at least one of the first, second, third, or fourth hard
bias layers contacts said free layer in the spin valve.

2. The hard bias structure of claim 1 wherein said first and third hard
bias layers are comprised of Co.sub.78.6Cr.sub.5.2Pt.sub.16.2, and the
second and fourth hard bias layers are comprised of
Co65Cr15Pt.sub.20.

3. A hard bias structure for providing a longitudinal bias to a free layer
in a spin valve within a magnetic read head, comprising:(a) a first
underlayer that has a body centered cubic (BCC) lattice structure and is
formed on a substrate and on either side of said spin valve;(b) a first
composite hard bias layer formed on the first underlayer and on either
side of a spin valve, comprising:(1) a first hard bias layer with a first
thickness, a coercivity (Hc), a top surface, and an Mrt value; and(2) a
second hard bias layer formed on the top surface of the first hard bias
layer, said second hard bias layer has a second thickness greater than
said first thickness, an Mrt value, and a coercivity greater than that of
the first hard bias layer;(c) a second underlayer formed on the first
composite hard bias layer; and(d) a second composite hard bias layer
formed on the second underlayer, comprising:(1) a third hard bias layer
with a top surface, and a first thickness, coercivity, and Mrt value
essentially the same as that of the first hard bias layer; and(2) a
fourth hard bias layer formed on the top surface of the third hard bias
layer, said fourth hard bias layer has a thickness, coercivity, and Mrt
value essentially the same as that of the second hard bias layer;wherein
at least one of the first, second, third, or fourth hard bias layers
contacts said free layer in the spin valve.

4. The hard bias structure of claim 3 wherein said first and third hard
bias layers are comprised of Co.sub.78.6Cr.sub.5.2Pt.sub.16.2, and the
second and fourth hard bias layers are comprised of
Co65Cr15Pt.sub.20.

5. The hard bias structure of claim 3 wherein said first and second
underlayers have the same composition that is one of FeCo, FeCoCr, FeCr,
FeV, FeTa, FePd, FeHf, FePt, or FeW.

6. A hard bias structure for providing a longitudinal bias to a free layer
in a spin valve within a magnetic read head, comprising:(a) a first
underlayer that has a body centered cubic (BCC) lattice structure and is
formed on a substrate and on either side of said spin valve; and(b) a
first CoXCrYPt.sub.Z layer with a first thickness formed on
said first underlayer wherein X, Y, and Z are the atomic % of Co, Cr, and
Pt, respectively, and wherein X+Y+Z=100 and X is about 65, Y is about 15,
and Z is about 20.

7. The hard bias structure of claim 6 wherein said first
CoXCrYPt.sub.Z layer is comprised of
Co65Cr15Pt20 and said hard bias structure is further
comprised of a second underlayer with a BCC lattice structure formed on
the first Co65Cr15Pt20 layer and a second
Co65Cr15Pt20 layer formed on the second underlayer.

8. A method of forming a hard bias structure in a magnetic read head based
on an MR element, comprising:(a) providing a substrate on which an MR
element having a top surface and two sides and that is comprised of a
free layer which has two sidewalls coincident with said sides is
formed;(b) forming a seed layer on said substrate and adjacent to each
side of said MR element;(c) depositing a first BCC underlayer on said
seed layer;(d) depositing a first composite hard bias layer on said first
BCC underlayer, said first composite hard bias layer comprises:(1) a
lower first hard bias layer that has a first thickness, coercivity, and a
top surface; and(2) a second hard bias layer formed on the top surface of
the lower first hard bias layer and having a second thickness greater
than the first thickness and a coercivity greater than that of the first
hard bias layer;(e) depositing a second BCC underlayer on the first
composite hard bias layer; and(f) depositing a second composite hard bias
layer on the second BCC underlayer, said second composite hard bias layer
comprises:(1) a lower third hard bias layer with a top surface, and a
thickness and coercivity essentially the same as the first hard bias
layer; and(2) a fourth hard bias layer formed on the top surface of the
third hard bias layer, said fourth hard bias layer has a thickness,
coercivity, and Mrt value essentially the same as that of the second hard
bias layer;wherein at least one of the first, second, third, or fourth
hard bias layers contacts said free layer in the spin valve.

9. The method of claim 8 wherein said first and third hard bias layers are
comprised of Co.sub.78.6Cr.sub.5.2Pt.sub.16.2, and the second and fourth
hard bias layers are comprised of Co65Cr15Pt.sub.20.

10. The method of claim 8 wherein said first and second underlayers have
the same composition that is one of FeCo, FeCoCr, FeCr, FeV, FeTa, FePd,
FeHf, FePt, or FeW.

11. A method of forming a hard bias structure in a magnetic read head
based on an MR element, comprising:(a) providing a substrate on which an
MR element having a top surface and two sides and that is comprised of a
free layer which has two sidewalls coincident with said sides is
formed;(b) forming a seed layer on said substrate and adjacent to each
side of said MR element;(c) forming a first BCC underlayer on said seed
layer; and(d) forming a first CoXCrYPt.sub.Z layer with a first
thickness that contacts a top surface of said first BCC underlayer
wherein X, Y, and Z are the atomic % of Co, Cr, and Pt, respectively, and
wherein X+Y+Z=100 and X is about 65, Y is about 15, and Z is about 20.

12. The method of claim 11 further comprised of forming a second BCC
underlayer on said first CoXCrYPt.sub.Z layer and forming a
second CoXCrYPt.sub.Z layer on the second BCC underlayer.

13. The method of claim 12 wherein said first CoXCrYPt.sub.Z
layer and second CoXCrYPt.sub.Z layer are comprised of
Co65Cr15Pt.sub.20.

Description:

[0001]This is a Divisional application of U.S. patent application Ser. No.
10/868,716, filed on Jun. 15, 2004, which is herein incorporated by
reference in its entirety, and assigned to a common assignee.

FIELD OF THE INVENTION

[0002]The invention relates to an improved hard bias structure formed
adjacent to a giant magnetoresistive (GMR) sensor in a magnetic read head
and a method for making the same. In particular, a composite hard bias
layer on a body centered cubic (BCC) underlayer is disclosed that
achieves a high coercivity while minimizing asymmetry sigma in a read
operation.

BACKGROUND OF THE INVENTION

[0003]A magnetic disk drive includes circular data tracks on a rotating
magnetic disk and read and write heads that may form a merged head on a
slider that is attached to a positioning arm. During a read or write
operation, the merged head is suspended over the magnetic disk on an air
bearing surface (ABS). The sensor in a read head is a critical component
in which different magnetic states are detected by passing a sense
current there through and monitoring a resistance change. One form of
magneto-resistance is a spin valve magnetoresistance (SVMR) or giant
magnetoresistance (GMR) which is based on a configuration in which two
ferromagnetic layers are separated by a non-magnetic conductive layer in
the sensor stack. One of the ferromagnetic layers is a pinned layer in
which the magnetization direction is fixed by exchange coupling with an
adjacent anti-ferromagnetic (AFM) pinning layer. The second ferromagnetic
layer is a free layer in which the magnetization vector can rotate in
response to external magnetic fields. In the absence of an external
magnetic field, the magnetization direction of the free layer is aligned
perpendicular to that of the pinned layer by the influence of abutting
hard bias layers. When an external magnetic field is applied by passing
the sensor over a recording medium on the ABS plane, the magnetic moment
of the free layer may rotate to a direction which is parallel to that of
the pinned layer. A sense current is used to detect a resistance value
which is lower when the magnetic moments of the free layer and pinned
layer are parallel.

[0004]In a CPP configuration, a sense current is passed through the sensor
in a direction perpendicular to the layers in the sensor stack.
Alternatively, there is a current-in-plane (CIP) configuration where the
sense current passes through the sensor in a direction parallel to the
planes of the layers in the sensor stack.

[0005]Ultra-high density (over 100 Gb/in2) recording requires a
highly sensitive read head in which the cross-sectional area of the
sensor is typically smaller than 0.1×0.1 microns at the ABS plane.
Current recording head applications are typically based on an abutting
junction configuration in which a hard bias layer is formed adjacent to
each side of a free layer in a GMR spin valve structure. As the recording
density further increases and track width decreases, the junction edge
stability becomes more important so that edge demagnification in the free
layer is prevented. In other words, horizontal (longitudinal) biasing is
necessary so that a single domain magnetization state in the free layer
will be stable against all reasonable perturbations. The critical
dimensions for sensor elements become smaller with higher recording
density requirements and therefore the minimum longitudinal bias field
necessary for free layer domain stabilization increases.

[0006]A high coercivity in the in-plane direction is needed in the hard
bias layer to provide a stable longitudinal bias that maintains a single
domain state in the free layer and thereby avoids undesirable Barkhausen
noise. By arranging the flux flow of the free layer to be equal to the
flux flow of the hard bias film, there are no magnetic poles at the
abutting junction edges and the demagnetizing field in that vicinity
becomes zero. This condition is realized when there is a sufficient
in-plane remnant magnetization (Mr) which may also be expressed as Mrt
since Mr is dependent on the thickness of the hard bias layer. Mrt is the
component that provides the longitudinal bias flux to the free layer and
must be high enough to assure a single magnetic domain in the free layer
but not so high as to prevent the magnetic field in the free layer from
rotating under the influence of a reasonably sized external magnetic
field. Moreover, a high saturation magnetization (Ms) and a high
squareness (S) value for Mr/Ms that approaches 1 in the hard bias layer
is desired.

[0007]Referring to FIG. 1, a conventional read head 1 based on a GMR
configuration is shown and is comprised of a substrate 2 upon which a
first shield layer 3 and a first gap layer 4 are formed. There is a GMR
element comprised of a bottom portion 5a, a free layer 6, and a top
portion 5b formed on the first gap layer 4. Note that the GMR element
generally has sloped sidewalls wherein the top portion 5b is not as wide
as the bottom portion 5a. The GMR element may be a bottom spin valve in
which an AFM pinning layer and pinned layer (not shown) are in the bottom
portion 5a or the GMR element may be a top spin valve where the AFM and
pinned layers are in the top portion 5b. There is a seed layer 7 formed
on the first gap layer 4 and along the GMR element which ensures that the
subsequently deposited hard bias layers 8 have a proper microstructure.
Hard bias layers 8 form an abutting junction 12 on either side of the
free layer 6. Leads 9 are provided on the hard bias layers 8 to carry
current to and from the GMR element. The distance between the leads 9
defines the track width TW of the read head 1. Above the leads 9 and GMR
element are successively formed a second gap layer 10 and a second shield
layer 11.

[0008]The pinned layer in the GMR element is pinned in the Y direction by
exchange coupling with an adjacent AFM layer that is magnetized in the Y
direction by an annealing process. The hard bias layers 8 which are made
of a material such as CoCrPt are magnetized in the X direction as
depicted by vectors 13 and influence an X directional alignment of the
magnetic vector 14 in the free layer 6. When a magnetic field of
sufficient strength is applied in the Y direction from a recording medium
by moving the read head 1 over a hard disk (not shown) in the Z
direction, then the magnetization in the free layer switches to the Y
direction. This change in magnetic state is sensed by a voltage change
due to a drop in the electrical resistance for an electrical current that
is passed through the MR element. In a CIP spin valve, this sense current
IS is in a direction parallel to the planes of the sensor stack.

[0009]One concern about the output from a spin valve element during a feed
back (read) operation is that the asymmetry sigma should be as small as
possible in order to accurately reproduce the waveform from the recording
medium. Asymmetry is determined by the variable magnetization direction
of the free layer. Ideally, the magnetic moment 14 of the free layer 6 is
orthogonal to the magnetic moment of the pinned layer when no external
magnetic field is present. However, the actual angle between the
aforementioned magnetic moments usually deviates somewhat from 90°
because of other magnetic forces in the GMR element and thereby produces
an asymmetric waveform in the output.

[0010]A soft magnetic film with a high saturation flux density and
comprised of FeCoMo is employed as a magnetic pole layer in U.S. Patent
Publication 2002/0150790. Referring to FIG. 2, those skilled in the art
would recognize that a FeCoMo layer can be used to modify the read head
in FIG. 1 by inserting a FeCoMo underlayer 15 with a high magnetic moment
between the seed layer 7 and the hard bias layer 8 (FIG. 2). The
underlayer 15 improves the biasing efficiency and serves to reduce output
asymmetry. A further improvement in signal amplitude and asymmetry is
expected if the FeCoMo layer (or moment) can be increased while the total
Mrt is maintained or further reduced and the coercivity is maintained.
Unfortunately, the thickness of a FeCoMo underlayer and the associated
magnetic moment contribution is limited because a thicker FeCoMo film
leads to a loss of coercivity (Hc) in the hard bias layer 8. Thus, a new
hard bias structure is needed which allows the thickness of a body
centered cubic (BCC) underlayer such as FeCoMo to be increased without
lowering HC in the adjacent hard bias layer. A combination of high
coercivity to enhance edge junction pinning efficiency and a higher
moment contribution from a BCC underlayer to further reduce asymmetry
sigma has not been achieved in prior art hard bias structures to our
knowledge.

[0011]In U.S. Pat. No. 6,643,107, the electrode layers on both sides of a
GMR element are extended toward the center of a bottom spin valve and are
located above a backed (conductive) layer on a free layer. This structure
prevents dead zones at the edges of the free layer and improves output
characteristics including asymmetry.

[0012]An MR sensor is described in U.S. Pat. No. 6,270,588 in which the
Hex angle that is the angle between the direction of the exchange
coupling magnetic bias applied to the pinned layer and the longitudinal
bias direction is more than 90° in at least a portion of the
pinned layer. As a result, improved wave shape and better wave symmetry
is achieved.

[0013]An insulating hard bias layer made of cobalt ferrite or the like is
used in U.S. Pat. No. 6,512,661 to avoid shunting of current away from a
MR sensor which occurs with a conductive hard bias layer. A larger flux
decay length is also provided which leads to a higher density recording
capability.

[0014]In U.S. Pat. No. 6,519,121, a spin valve sensor with a composite
pinned layer to improve biasing of the free layer is described. A CoFeHfO
layer is formed on an AFM layer and a CoFe layer is formed on the CoFeHfO
layer and adjacent to a spacer layer in a MR element. This configuration
minimizes sense current shunting and improves the magnetoresistive
effect.

SUMMARY OF THE INVENTION

[0015]One objective of the present invention is to provide a hard bias
structure in which the thickness of a BCC underlayer component is
increased to enhance its moment contribution while maintaining a high
coercivity (Hc) for the hard bias structure.

[0016]A further objective of the present invention is to provide a
composite hard bias layer that has a high Hc value and has good lattice
matching with a BCC underlayer formed according to the first objective.

[0017]A still further objective of the present invention is to provide a
method of making a hard bias structure that is comprised of a BCC
underlayer and one or more hard bias layers in order to provide optimum
Hc and Mrt values and a reduced asymmetry output.

[0018]These objectives are achieved in a first embodiment in which a GMR
element with sidewalls and a top surface is formed on a first gap layer
on a substrate in a magnetic read head. The GMR element can have a top
spin valve or a bottom spin valve structure that is formed along an ABS
plane and is comprised of an AFM layer, a pinned layer, a free layer, and
a top surface that may be on a capping layer. The pinned layer is pinned
in a first direction perpendicular to the ABS plane and parallel to the
top surface of the substrate by exchange coupling with the magnetized AFM
layer. A seed layer with a body centered cubic (BCC) lattice structure is
formed on the first gap layer adjacent to the GMR element. A hard bias
structure is formed on a seed layer along each side of the GMR element
and contacts a substantial portion of the sidewalls in the GMR element to
form abutting junctions with the free layer. In one aspect, the hard bias
structure is comprised of a BCC underlayer and a composite hard bias
layer that has a lower Co78.6Cr5.2Pt16.2 layer and an
upper Co65Cr15Pt20 layer. Alternatively, the hard bias
structure comprises a BCC underlayer and an overlying
Co65Cr15Pt20 layer. The BCC underlayer is preferably a
ferromagnetic layer made of FeCoMo, for example, with a high magnetic
moment and that has good lattice matching with the overlying hard bias
layer.

[0019]The hard bias structure is magnetized in a direction orthogonal to
that of the pinned layer and parallel to the top surface of the
substrate. The hard bias structure is magnetically coupled to the free
layer and provides a longitudinal (in-plane) bias that enables a single
magnetic domain within the free layer. Electrical leads are formed above
the hard bias structure and contact the GMR element along its sidewalls
near the top surface of the capping layer. A second gap layer is formed
on the leads and on the GMR element and a second shield layer is formed
on the second gap layer to complete the magnetic read head.

[0020]In a second embodiment, the magnetic read head includes the same
layers as in the first embodiment except that the hard bias structure is
laminated such that the BCC
underlayer/Co78.6Cr5.2Pt16.2/Co65Cr15Pt20
configuration is repeated a plurality of times. Alternatively, the BCC
underlayer/Co65Cr15Pt20 configuration is repeated a
plurality of times. The thickness of the individual layers may be
adjusted so that the hard bias structure has optimum Hc and Mrt values
and provides a stable longitudinal bias to an adjacent free layer in the
GMR element.

[0021]The present invention is also a method of forming a magnetic read
head comprised of an improved hard bias structure according to the first
and second embodiments. A stack of GMR layers comprised of a free layer,
pinned layer, an AFM layer, and a cap layer is formed on a first gap
layer on a substrate by a conventional method. Known methods are also
employed to pattern a photoresist mask above the cap layer in the GMR
stack. An etch process is used to define a GMR element and a track width.
A seed layer is deposited on exposed portions of the first gap layer
adjacent to the GMR element. An important step is formation of a hard
bias structure on the seed layer and along a substantial portion of the
sidewalls on the GMR element. The hard bias structure is formed by a
magnetron sputtering or ion beam deposition (IBD) method that
sequentially forms a BCC underlayer and a hard bias layer comprised of
Co65Cr15Pt20 or a
Co78.6Cr5.2Pt16.2/Co65Cr15Pt20
configuration.

[0022]Alternatively, the hard bias structure may be laminated in which the
BCC underlayer/Co78.6Cr5.2Pt16.2/Co65Cr15Pt20 configuration or the BCC underlayer/Co65Cr15Pt20
configuration is repeated a plurality of times. The thicknesses of the
individual layers within the hard bias structure are adjusted to provide
optimum Hc and Mrt values while minimizing the asymmetry sigma in the
output signal during a read operation.

[0023]The hard bias structure may be magnetically aligned in a direction
parallel to the top surface of the GMR element and parallel to the ABS by
applying an external magnetic field during or after the deposition step.
Electrical leads are subsequently formed on the hard bias structure by a
conventional method. The photoresist layer is then removed by a lift-off
process, for example. The second gap layer and second shield layer are
sequentially formed on the electrical leads and GMR element by well known
methods.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a cross-sectional view showing a prior art magnetic read
head with a GMR element, a seed layer formed on a gap layer and along the
sidewalls of the GMR element, and a hard bias layer on the seed layer.

[0025]FIG. 2 is a cross-sectional view of a prior art magnetic read head
in which a hard bias structure comprised of a hard bias layer and an
underlayer is formed on a seed layer and adjacent to a GMR element.

[0026]FIG. 3 is a cross-sectional view that shows an intermediate step in
the method of forming a hard bias structure in a magnetic read head
according to a first embodiment of the present invention.

[0027]FIG. 4 is a cross-sectional view of a magnetic read head in which a
hard bias structure comprised of a CoCrPt composite hard bias layer is
formed on an underlayer and adjacent to a free layer in a GMR element.

[0028]FIG. 5 is a cross-sectional view that depicts an intermediate step
in the method of forming a laminated hard bias structure in a magnetic
read head according to a second embodiment of the present invention.

[0029]FIG. 6 is a cross-sectional view of a magnetic read head in which a
laminated hard bias structure comprised of a CoCrPt composite hard bias
layer on a BCC underlayer is formed adjacent to a GMR element according
to the second embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0030]The present invention is an improved hard bias structure in a
magnetic read head that has a high coercivity and a low output asymmetry
during a read operation. The hard bias structure is useful in magnetic
read heads that are based on CIP spin valves or CPP spin valves and is
also applicable to MTJ devices or multi-player sensor designs as
appreciated by those skilled in the art. The drawings are provided by way
of example and are not intended to limit the scope of the invention. For
example, the shape of a GMR element in the read head is not a limitation
and the present invention is equally applicable to any configuration
where a hard bias structure according to the first or second embodiment
forms an abutting junction with a free layer in a GMR element. Moreover,
the GMR element may be comprised of either a top spin valve or a bottom
spin valve. The present invention is also a method of forming a magnetic
read head with a hard bias structure according to the first or second
embodiment that has high Hc and S values and sufficient in-plane flux
density to ensure a single magnetic domain state in an adjacent free
layer.

[0031]A first embodiment is depicted in FIGS. 3-4. Referring to FIG. 3, a
cross-sectional view from an ABS plane is shown of a magnetic read head
20 which has a substrate 21 that may be a ceramic layer, for example. A
first shield layer 22 is formed on the substrate 21 and a first gap layer
23 is formed on the first shield layer by a conventional method. There is
a GMR element which is a stack comprised of a bottom portion 24, a free
layer 25, and a top portion 26 sequentially formed on the first gap layer
23. The GMR element typically has sloped sidewalls wherein the top
portion 26 has a smaller width than the bottom portion 24.

[0032]The GMR element is fabricated by sequentially depositing the layers
within the bottom portion 24, the free layer 25, and the layers within
the top portion 26 by a sputtering technique, for example, which is well
known in the art. A photoresist layer 27 is patterned on the top portion
26 and then an etch process is used to remove regions of the GMR stack
that are not covered by the photoresist layer 27. The etch stops on the
first gap layer 23 which may be Al2O3 or silicon oxide. Note
that the photoresist layer 27 typically has an undercut along both sides
at its interface with the top portion 26 of the GMR element to facilitate
a subsequent lift-off removal step.

[0033]In one embodiment that represents a bottom spin valve, the bottom
portion 24 is comprised of a seed layer such as NiCr on which an
anti-ferromagnetic (AFM) pinning layer, a pinned layer, and a spacer
layer which may be Cu are sequentially formed. The individual layers
within the bottom portion 24 are not shown in order to simplify the
drawing and direct attention to the abutting junction between the free
layer 25 and the subsequently deposited hard bias structure. The AFM
layer may be a PtMn or IrMn layer that is magnetized in the y direction.
The AFM layer is exchange coupled to the pinned layer that may be
comprised of CoFe and which is pinned in the y direction.

[0034]Optionally, the pinned layer may have a synthetic anti-parallel
(SyAP) configuration in which a coupling layer such as Ru is sandwiched
between an AP2 pinned layer on the AFM layer and an overlying AP1 pinned
layer. The AP2 layer has a magnetic moment or vector oriented in the y
direction by exchange coupling with an AFM pinning layer. The AP1 layer
is adjacent to the spacer and is anti-parallel exchange coupled to the
AP2 layer via the coupling layer as is understood by those skilled in the
art. Thus, the magnetic moment or vector of the AP1 pinned layer is
oriented in the "-y" direction which is anti-parallel to the magnetic
vector of the AP2 layer. The magnetic moments of the AP2 and AP1 layers
combine to produce a net magnetic moment that is less than the magnetic
moment of a single pinned layer. A small net magnetic moment results in
improved exchange coupling between the AP2 layer and the AFM layer and
also reduces interlayer coupling between the AP1 layer and the free layer
25.

[0035]The free layer 25 may be comprised of CoFe and/or NiFe, for example,
and has a thickness of about 20 to 50 Angstroms. The magnetization of the
free layer 25 is oriented in the x direction under the influence of a
longitudinal bias from the adjoining hard bias structure which is
magnetized in the x direction and will be described in a later section.
In the bottom spin valve structure, the top portion 26 of the GMR element
is comprised of a cap layer such as Ta or Ru, for example. Optionally,
the cap layer may be comprised of more than one layer such as a layer of
NiCr on a layer of tantalum oxide.

[0036]In an alternative embodiment that represents a top spin valve, the
bottom portion 24 may be comprised of a seed layer such as NiCr and an
optional buffer layer (not shown) in which a layer of Ru is formed on the
seed layer and a copper layer is formed on the Ru layer to provide a
lattice match to the overlying free layer 25. The magnetization and
composition of the free layer 25 are the same as described previously.
Above the free layer in the top portion 26 are sequentially formed a
spacer, a pinned layer which may have a SyAP configuration, an AFM layer,
and a cap layer. The aforementioned layers have the same composition and
magnetization direction as in the previously described bottom portion of
the bottom spin valve structure. The layers in the top portion 26 of the
top spin valve embodiment are not shown in order to simplify the drawing
and direct attention to the abutting junction formed between the free
layer 25 and the hard bias structure on either side of the GMR element.

[0037]In the presence of an appropriately sized external magnetic field
which can be applied when the magnetic head 20 is passed over a magnetic
recording medium in the z direction, the magnetization direction in the
free layer 25 switches to the y or -y direction. The changed magnetic
state in the free layer 25 may be sensed by passing a current through the
GMR element to detect a lower resistance than when the magnetization of
the pinned layer and free layer are orthogonal to each other.

[0038]Next, a seed layer 28 such as CrTi with a thickness between about 10
and 100 Angstroms and preferably about 30 Angstroms is deposited on the
first gap layer 23 by a sputtering method or ion beam deposition (IBD).
Alternatively, the seed layer 28 may be one of TiW, CrMo, or other
materials that have a body centered cubic (BCC) lattice structure and
have good lattice matching with a subsequently deposited underlayer and
hard bias layer.

[0039]An important feature of the present invention is the hard bias
structure 32 which is deposited on the seed layer 28. In one aspect, the
hard bias structure 32 is comprised of a stack of layers including an
underlayer 29 formed on the seed layer 28 and a composite hard bias layer
disposed on the underlayer 29. The composite hard bias layer consists of
a lower hard bias layer 30 hereafter referred to as HB1 and an upper hard
bias layer 31 hereafter referred to as HB2. In the exemplary embodiment,
the hard bias structure is formed by a sputtering or IBD method.
Optionally, the composite hard bias layer may be formed directly on the
seed layer 28 by omitting the underlayer 29 although this arrangement is
generally less desirable.

[0040]In one embodiment, the underlayer 29 is a FeCoMo layer that has a
composition represented by FeRCoSMoT wherein R, S, and T
are the atomic % of Fe, Co, and Mo, respectively, and wherein R+S+T=100
and R is from about 10 to 90, S is between about 10 and 90, and T is from
about 5 to 20. Preferably, the thickness of the underlayer 29 is from
about 5 to 40 Angstroms but may vary depending upon the desired thickness
of the hard bias structure and the thickness of the overlying composite
hard bias layer. The underlayer 29 has a high magnetic moment and a
lattice structure intermediate between that of the seed layer 28 and the
HB1 layer 30 in order to provide good lattice matching. Optionally, the
underlayer 29 may be made of a BCC ferromagnetic material such as FeCo,
FeCoCr, FeCr, FeV, FeTa, FePd, FeHf, FePt, FeW, or the like that has a
high magnetic moment represented by the equation 4πMs≧10000 and
which has good lattice matching with hard bias layers such as those based
on a CoCrPt alloy.

[0041]In one embodiment, the HB1 layer 30 is comprised of a CoCrPt alloy
that has a composition represented by CoXCrYPt.sub.Z in which
X, Y, and Z are the atomic % of Co, Cr, and Pt, respectively, and wherein
X+Y+Z=100 and X is from about 50 to 80, Y is between 0 and about 20, and
Z is from 0 to about 50. Preferably, the HB1 layer 30 has a composition
that is 78.6 atomic % Co, 5.2 atomic % Cr, and 16.2 atomic % Pt which is
hereafter referred to as Co78.6Cr5.2Pt16.2. This
composition is typically employed in prior art CoCrPt hard bias layers.
The Cr component serves to improve corrosion resistance and magnetic
domain structure while the Pt component is used to control coercivity.
The thickness of the HB1 layer 30 is from about 10 to 50 Angstroms. The
thickness may be adjusted to optimize the Hc, Mrt, and S values for the
hard bias structure 32. It is understood that each of the layers in the
hard bias structure 32 has a Hc, Mrt, and S component and that magnetic
coupling between the layers produces Hc, Mrt, and S values for the hard
bias structure that influences the adjacent free layer 25 and ensures a
single domain state formed therein. Note that the CoCrPt alloy of the
present invention encompasses a CoPt layer (Y=0) and a CoCr layer (Z=0).

[0042]Alternatively, the HB1 layer 30 may be comprised of another material
such as FePt that has a high coercivity and good lattice matching with a
BCC underlayer 29 and with a BCC seed layer 28. Preferably, the HB1 layer
has a minimum Hc value of greater than 1000 Oe and has an Mrt value in
the range of about 0.1 to 0.5.

[0043]In the embodiment where the HB1 layer 30 is comprised of a
Co78.6Cr5.2Pt16.2 layer, the HB2 layer 31 preferably has a
thickness between about 50 and 300 Angstroms and a composition
represented by CoXCrYPt.sub.Z in which X, Y, and Z are the
atomic % of Co, Cr, and Pt, respectively, and wherein X+Y+Z=100 and X is
about 65, Y is about 15, and Z is about 20 which is hereafter referred to
as Co65Cr15Pt20. The inventors have surprisingly found
that a composite hard bias layer with a
Co78.6Cr5.2Pt16.2/Co65Cr15Pt20 (HB1/HB2)
configuration has a higher coercivity than a single hard bias layer based
on a Co78.6Cr5.2Pt16.2 alloy. As shown in Table 1, the
thickness of the HB2 layer 31 may also be adjusted to optimize HC
and Mrt values for the hard bias structure 32. Preferably, the HB2 layer
31 thickness is about 2 to 10 times that of the HB1 layer 30 thickness
and the combined thicknesses of the HB1 and HB2 layers is between about
150 and 350 Angstroms. At least one of the HB1 and HB2 layers 30, 31
forms an abutting junction with the free layer 25 in the GMR element. A
higher Cr content in the HB2 layer provides for more grain segregation
while a higher Pt content provides for a higher coercivity and lower
moment than in the HB1 layer.

[0044]In Table 1, samples S1 and S3 are examples of prior art hard bias
structures previously employed by the inventors. Note that while the
insertion of a FeCoMo underlayer in S3 has the desired effect of
increasing Mrt (memμ/cm2) compared to that of S1, the Hc value
suffers a substantial reduction. One advantage of the present invention
is that when no underlayer is present on the seed layer, a composite hard
bias layer such as the one represented by the
Co78.6Cr5.2Pt16.2/Co65Cr15Pt20 (HB1/HB2)
configuration in S2 provides a higher coercivity than a single
Co78.6Cr5.2Pt16.2 hard bias layer in S1. This advantage
also holds for the
Co78.6Cr5.2Pt16.2/Co65Cr15Pt20
configuration on a FeCoMo underlayer (S4) compared to a
Co78.6Cr5.2Pt16.2/FeCoMo stack in S3. Thus, in a hard bias
structure where a BCC underlayer is inserted to increase Mrt, the
composite hard bias layer of the present invention is able to increase
the coercivity (Hc) with a minimal effect on Mrt. Furthermore, the
inventors have verified that asymmetry sigma is lowered when a composite
HB1/HB2 hard bias layer of the present invention is incorporated in a
hard bias structure with a BCC underlayer.

[0045]Samples S5, S6, and S7 show various thicknesses for the HB1 and HB2
layers and demonstrate that the Mrt can be fine tuned to provide an
optimum value for Hc which in this case occurs for sample S4. Meanwhile,
a high squareness (S) value and a high coercive force angle ratio (S*)
are maintained in all samples with the HB1/HB2 composite hard bias layer.
A second advantage as a result of the capability to fine tune the Mrt
value is that a higher process window may be realized when forming the
hard bias structure. In other words, by simultaneously optimizing Mrt and
Hc, small variations in the thickness of the layers within the hard bias
structure 32 will have a minimal effect on Mrt and Hc.

[0046]In an alternative embodiment where the HB1 layer 30 is formed of a
material other than a CoCrPt alloy, a HB2 layer 31 composition is
selected that has a high coercivity, a magnetic moment similar to that of
Co65Cr15Pt20 and which provides good lattice matching with
the HB1 layer. Furthermore, the HB1 and HB2 layer requirements and
relationships described earlier are also applicable in this case. The
thicknesses of the HB1 and HB2 layers 30, 31 may be adjusted to optimize
Hc and Mrt values for the hard bias structure 32.

[0047]The present invention also encompasses a hard bias structure 32
wherein the HB2 layer 31 is formed directly on the BCC underlayer 29 and
has a composition represented by CoXCrYPt.sub.Z in which X, Y,
and Z are the atomic % of Co, Cr, and Pt, respectively, and wherein
X+Y+Z=100 and X is about 65, Y is about 15, and Z is about 20.
Preferably, the HB2 layer 31 is a Co65Cr15Pt20 layer. In
other words, the thickness (and moment contribution) from the HB1 layer
30 can be reduced to zero. Since a Co65Cr15Pt20 layer has
a smaller magnetic moment (˜40% less) than a
Co78.6Cr5.2Pt16.2 layer, the thickness of the HB2 layer 31
is increased in order to match the total Mrt of a composite
Co78.6Cr5.2Pt16.2/Co65Cr15Pt20 layer.
Optionally, the HB2 layer is made thicker to match the Mrt of a
Co78.6Cr8.2Pt16.2 layer such as sample S1 that is used in
the prior art. The HB2 layer when formed on the BCC underlayer 29 may
have a thickness in the range of about 50 to 300 Angstroms. As a result
of the thicker Co65Cr15Pt20 layer along the junction edge
with the free layer 25, the junction coverage will be more uniform and
the coercivity of the HB2 layer 31 along the tapered junction edge will
be larger. Furthermore, a Co65Cr15Pt20 layer has smaller
anisotropy energy than a Co78.6Cr5.2Pt16.2 layer and
therefore tends to have less easy axis dispersions when it is exchanged
coupled with a magnetic underlayer such as FeCoMo. The inventors have
surprisingly found improved performance when a
Co65Cr15Pt20/FeCoMo hard bias structure is substituted for
the Co78.8Cr5.2Pt16.2/FeCoMo configuration in sample S3
(Table 1).

[0048]The properties of the hard bias structure of the present invention
are very stable with or without annealing. Although no annealing is
necessary, the hard bias structure 32 may be annealed by heating the
substrate 21 at a temperature of about 200° C. to 250° C.
in a N2 ambient for a period of about 0.5 to 5 hours.

[0049]An electrical lead 33 is deposited by a sputtering or IBD method on
the HB2 layer 31 on each side of the GMR element. Although the leads 33
are connected to the sides of the GMR element on the top portion 26 in
the exemplary embodiment, the present invention also anticipates a
configuration in which the leads are attached to the top surface 26a
(FIG. 4) of the top portion. The leads may be a composite layer in which
a thicker conductive layer such as Au or Cu is sandwiched between thinner
Ta layers. In one embodiment (not shown), the leads 29 are comprised of a
30 Angstrom thick first Ta layer on the HB2 layer 31, a 400 Angstrom
thick gold or copper layer on the first Ta layer, and a 30 Angstrom thick
second Ta layer on the gold or copper layer. The bottom Ta layer serves
as an interrupt layer to provide a good crystallographic match between
the HB2 layer 31 and the gold or copper lead layer.

[0050]Referring to FIG. 4, a conventional lift-off process is used to
remove the photoresist layer 27 and the overlying seed layer 28,
underlayer 29, HB1 and HB2 layers 30, 31 and the lead layer 33. A track
width TW is defined as the distance between the leads 33 on the top
surface 26a of the GMR element. A second gap layer 34 is disposed on the
leads 33 and top portion 26 and a second shield layer 35 is formed on the
second gap layer 34 to complete the magnetic read head 20. Note that the
second shield layer 35 preferably has a smooth top surface in order to
improve the process latitude for subsequent process steps that could
involve a write head fabrication as an example.

[0051]A second embodiment will now be described in which a hard bias
structure formed adjacent to a free layer in a magnetoresistive (MR)
element is comprised of laminated hard bias layers. In the exemplary
embodiment pictured in FIGS. 5-6, the hard bias structure is formed in a
magnetic read head and adjacent to a GMR element that was described
previously in the first embodiment. However, the second embodiment also
encompasses any configuration where a hard bias structure described
herein forms an abutting junction with a free layer in a MR element.

[0052]Referring to FIG. 5, a first shield layer 22 and a first gap layer
23 are provided on a substrate 21 as previously described. Likewise, a
GMR element comprised of a bottom portion 24, a free layer 25, and a top
portion 26 is then fabricated on the first gap layer according to a
method described in the first embodiment in which a patterned photoresist
layer 27 having a width w serves as an etch mask. A seed layer 28
comprised of CrTi with a thickness of about 30 Angstroms is deposited on
the exposed regions of the first gap layer 23 by a sputtering or IBD
process. Alternatively, the seed layer 28 may be one of TiW, CrMo, or
another material that has a body centered cubic (BCC) lattice structure
and good lattice matching with a subsequently deposited underlayer and
hard bias layer.

[0053]An important feature of the present invention is the hard bias
structure 40 which is deposited on the seed layer 28. In one aspect, the
hard bias structure 40 is made of laminated layers in which a stack
comprised of an underlayer 29 and a composite hard bias layer on the
underlayer is repeated two or more times to form a plurality of stacks.
For example, a bottom layer in a second stack is formed on the top layer
of a first stack and so forth. Optionally, the underlayer 29 may be
omitted from one or more stacks in the hard bias structure although this
arrangement is generally less desirable. In the exemplary embodiment, a
second stack of three layers is formed on a first stack of three layers.
However, more than two stacks of layers may be formed as appreciated by
those skilled in the art. The laminated hard bias structure 40 is
fabricated by a conventional means which may involve magnetron
sputtering, for example.

[0054]The first stack of three layers in the hard bias structure 40
consists of an underlayer 29a, a lower hard bias (HB1) layer 30a, and an
upper hard bias (HB2) layer 31a. In one aspect, the underlayer 29a is a
FeCoMo layer that has a composition represented by
FeRCoSMoT wherein R, S, and T are the atomic % of Fe, Co,
and Mo, respectively, and wherein R+S+T=100 and R is from about 10 to 90,
S is between about 10 and 90, and T is from about 5 to 20. Preferably,
the thickness of the underlayer 29a is from about 5 to 40 Angstroms but
may vary depending upon the desired thickness of the hard bias structure,
the number of stacks employed, and the thickness of the overlying
composite hard bias layer. The underlayer 29a has a high magnetic moment
and a lattice structure intermediate between that of the seed layer 28
and the HB1 layer 30a in order to provide good lattice matching.
Optionally, the underlayer 29a may be made of a BCC ferromagnetic
material such as FeCo, FeCoCr, FeCr, FeV, FeTa, FePd, FeHf, FePt, FeW, or
the like that has a high magnetic moment represented by the equation
4πMs≧10000 and which has good lattice matching with hard bias
layers such as those based on a CoCrPt alloy.

[0055]In one embodiment, the HB1 layer 30a is comprised of a CoCrPt alloy
that has a composition represented by CoXCrYPt.sub.Z in which
X, Y, and Z are the atomic % of Co, Cr, and Pt, respectively, and wherein
X+Y+Z=100 and X is from about 50 to 80, Y is between 0 and about 20, and
Z is from 0 to about 50. Preferably, the HB1 layer 30a is a
Co78.6Cr5.2Pt16.2 layer. The thickness of the HB1 layer
30a is from about 10 to 50 Angstroms but may vary depending on the number
of stacks in the laminated hard bias structure and may be adjusted to
optimize the Hc, Mrt, and S values for the hard bias structure 40. It is
understood that each of the layers in the hard bias structure 40 has a
Hc, Mrt, and S component and that magnetic coupling between the layers
produces Hc, Mrt, and S values for the hard bias structure that
influences the adjacent free layer 25 and ensures a single domain state
formed therein.

[0056]Alternatively, the HB1 layer 30a may be comprised of another
material such as FePt that has a high coercivity and good lattice
matching with a BCC underlayer 29a and with a BCC seed layer 28.
Preferably, the HB1 layer has a minimum Hc value of greater than 1000 Oe
and has an Mrt value in the range of about 0.1 to 0.5.

[0057]In the embodiment where the HB1 layer 30a is comprised of a
Co78.6Cr5.2Pt16.2 layer, the HB2 layer 31a preferably has
a thickness between about 50 and 300 Angstroms and is a
Co65Cr15Pt20 layer. The inventors have unexpectedly found
that a composite hard bias layer with a
Co78.6Cr5.2Pt16.2/Co65Cr15Pt20 (HB1/HB2)
configuration has a higher coercivity than a single hard bias layer based
on a Co78.6Cr5.2Pt16.2 alloy. The thickness of the HB2
layer 31a may also be adjusted to optimize HC and Mrt values in the
hard bias structure 40. Preferably, the HB2 layer 31a thickness is about
2 to 10 times that of the HB1 layer 30a thickness and the combined
thicknesses of the HB1 and HB2 layers in the first stack is between about
150 and 350 Angstroms.

[0058]In an alternative embodiment where the HB1 layer 30a is formed of a
material other than a CoCrPt alloy, a HB2 layer 31a composition is
selected that has a high coercivity, a magnetic moment similar to that of
Co65Cr15Pt20 and which provides good lattice matching with
the HB1 layer and with a subsequently formed underlayer 29b in the second
stack.

[0059]A second stack of layers is formed on the HB2 layer 31a and is
comprised of from bottom to top in order, a second underlayer 29b, a
second HB1 layer 30b, and a second HB2 layer 31b. The composition and
film thickness of the second underlayer 29b is preferably the same as
that described for the underlayer 29a. Similarly, the composition and
thickness of the second HB1 layer 30b and the second HB2 layer 31b are
preferably the same as the composition and thickness of the hard bias
layers 30a, 31a respectively. However, the thickness and composition of
each of the layers in the first and second stack may be adjusted to
provide optimum Hc and Mrt values for the hard bias structure 40. Note
that at least one of the layers in the hard bias structure forms an
abutting junction with an adjacent free layer.

[0060]The present invention also encompasses a laminated hard bias
structure 40 wherein the HB2 layers 31a, 31b are preferably
Co65Cr15Pt20 layers and are formed directly on the BCC
underlayers 29a, 29b, respectively. In other words, the thickness (and
moment contribution) from the HB1 layers 30a, 30b can be reduced to zero
and the second underlayer 29b is formed on first HB2 layer 31a. Since a
Co65Cr15Pt20 layer has a smaller magnetic moment
(˜40% less) than a Co78.6Cr5.2Pt16.2 layer, the
thicknesses of the HB2 layers 31a, 31b are increased accordingly in order
to match the total Mrt of a Co78.6Cr5.2Pt16.2 layer or a
composite Co78.6Cr5.2Pt16.2/Co65Cr15Pt20
layer as referred to in Table 1. At least one of the HB2 layers 31a, 31b
adjoins each side of the free layer 25. The advantages of a hard bias
structure comprised of a BCC underlayer/Co65Cr15Pt20
configuration are similar to those mentioned in the first embodiment.

[0061]Although no annealing is necessary to stabilize the properties of
the layers within the hard bias structure 40, the hard bias structure may
be annealed by heating the substrate 21 at a temperature of about
200° C. to 250° C. in a N2 ambient for a period of
about 0.5 to 5 hours.

[0062]Electrical leads 33 are formed on the hard bias structure 40 by a
conventional process. In one embodiment, the leads 33 are comprised of a
composite Ta/Au/Ta layer in which a 30 Angstrom thick first Ta layer is
sputter deposited on the hard bias structure 40, a 400 Angstrom thick Au
layer is sputter deposited on the first Ta layer, and a 30 Angstrom thick
second Ta layer is sputter deposited on the Au layer. Optionally, Cu may
be used in place of Au in the lead layer. Although the leads 33 are shown
connected to the sides of the top portion 26 of the GMR element, the
invention also anticipates a configuration in which the leads are
attached to the top surface 26a of the top portion 26.

[0063]Referring to FIG. 6, the photoresist layer 27 and overlying seed
layer 28, hard bias structure 40, and lead 33 are removed by a well known
lift off process to leave the top surface of the top portion 26 exposed
between the leads 33. A second gap layer 34 is deposited on the leads 33
and top portion 26 as described previously. Subsequently, a second shield
layer 35 is formed on the second gap layer 34 according to the process
included in the first embodiment.

[0064]The advantages of the second embodiment are the same as described in
the first embodiment. First, the hard bias structure of the present
invention provides a higher coercivity than a single hard bias layer
based on Co78.6Cr5.2Pt16.2 or CoPt in the prior art.
Moreover, in a hard bias structure where a BCC underlayer is inserted to
increase Mrt, the hard bias structure of the present invention is able to
increase the coercivity (Hc) with a minimal effect on Mrt. In other
words, the loss in Hc due to insertion of an underlayer in the hard bias
structure of the present invention is compensated by the higher initial
Hc value generated by the composite hard bias layer or by a thicker
Co65Cr15Pt20 layer. As a result, the output asymmetry is
reduced during a read operation.

[0065]Another advantage is the capability to fine tune the Mrt value so
that a higher process window may be realized when forming the hard bias
structure. Therefore, small variations in the thickness of the various
layers within the hard bias structure will have a minimal effect on the
magnitude of the Hc and Mrt values.

[0066]While this invention has been particularly shown and described with
reference to, the preferred embodiment thereof, it will be understood by
those skilled in the art that various changes in form and details may be
made without departing from the spirit and scope of this invention.